The present invention relates to a method for measuring the resistance of a winding of a converter-fed single- or three-phase machine during operation by means of a d-c measuring current present as the d-c component of the phase current, and to a circuit arrangement for carrying out the method.
From German Patent No. 32 28 815, a circuit arrangement with a d-c measuring voltage source for a winding fed with operating currents of network frequency is known. In at least one of the connecting leads between the network and the winding of a single- or three-phase machine, a non-linear resistance circuit operative only during the measuring time is arranged as the d-c measuring voltage source. The resistance value of this nonlinear resistance circuit changes greatly as a function of the polarity of the operating current of network frequency flowing through it. The d-c voltage component generated in this manner is fed as the d-c measuring voltage, in addition to the winding, to a measuring member which picks up only the d-c voltage. A variable low-resistance resistor with a shunt diode and a shorting switch for the parallel arrangement of the resistor and the diode is provided as the nonlinear resistance circuit, for instance. In this circuit arrangement, the nonlinear resistance circuit must be designed for the full operating current. The nonlinear resistance circuit further causes additional losses during the measurement.